Transmission control



'NOV. 3, 1931. BJORNSON 1,830,220

TRANSMISSION CONTROL Filed July 9, 1930 INVENTUR B. [3. BJORNSUN ATTORNEY Patented Nov. 3, 1931 moan. s. isaomvsoiv, or NEW- ORK, .Y.,

-nssreivon TO. IBELLQTELEI'HONE LABORA- roams, Inoonron'nrnn, or'nEwYonK; m n, A CORPORATION on NEW YORK f f EritAnsMIssIoN joon'rnon Application filed July 9,

This invention relates to two-way signaling systems and particularly to means for. I I controlling transmission insuchsystems.

1 an objecto'fthe invention is tolmprove the n 7 operation oftafsignal transmission system in;

cluding therein circuit-control means operated under control of thesignalsftransmitted over thesystem. 7' 1 The invention is specially applicable to a system over which. two-way transmission of signaling energy is requiredwithin the same frequency range, and including as a link therein a two-way cable of high attenuation transmission in the opposite direction.

The relatively long time i-(as compared to radio circuits, for example) required for transmitting signals overthe cable in a system 7 such as has just been" described greatly 1ncreases the chance that two 'subscribers'at'the ends of the system may bothstart talking within'a time interval equal to the overall 'tr'ansmissiontime oi the cable resulting in ea ch'subscriber seizing control of the circuit control apparatus at'his own terminal and locking out the transmision of the other Subrs-criber. r Circuits have heretofore 'been desi nod to avoid the abovementioned difficulty y giving complete control of the circuit-control apparatus at both ends offthe system to that subscriberwho first starts talking. This in vention relates to an improved circuit of that type, theimpr'ovement residing inmeans for facilitating break-ins by a listening party after one party hasobtained control; Specifically stated,'the invention comprises means reown spee out. and hightransmissiontime-constant,such as a deep sea submarine telephone cable; Sig- 1930; Serial No. 466,121; r

'sponsive to the signals of the first talker and operative a definiteti-me after he has obtained complete control of the system, for making certain circuit changes at the teminals which will'bias the system from thestandpoint of break-ins in'favor of the listener and maintain that biasfor a definite time after the first talker-ceases to talk. While the circuitsare so biased, the listenercan, on perceiving a pause by the first talker, immediately break-in, gain control of the system'for his 0 currents and shut the first talker I The'invention :is especially adapted for, although not limited to, two-way signaling systems whichemploy these-called courier method of transmission control for prevent ing transmission lock-outs, such as described in the copending applications of R. C. Mathes, Serial Nos. 37 0,034: and 37 0,035, both filed June 11 1929'and in my copendingap- 9, 1930 and 425,092 filed February 1, 1930.

'l he exact nature and advantages'of the invention will be clear vfrom the following detailed description thereof when read in plications, Serial Nos; 419,668 filed J anuary connection with the accompanying drawing I diagram'of one terminal station for a sub marine cable telephone system embodying the invention.

For conveniencethe invention will be described as applied to a system for the two- Way transmission of speech waves, but it is to be understood that-the principles of the invention apply equally well to systems for the two-way transmission'of signal waves in gener'al of frequencies within or outside the speech frequency range, such as waves representing speech, entertainment programs comprising music as well as speech, etc.

Since the terminal stationat eachend of the cable in the svstem to be described may be substantially identical in construction except for changes in the design of the courier wave generators andthe filters used therein,

necessitated by the'fact that the values of'the frequencies of thecourier waves transmitted from the two terminals are different, it has thesingle figure of which shows a circuit been deemed'jsulhcient to illustrate only one terminal of the cable system.

tenirof transmission control of the general 7 type disclosed in Fig. 2 ofthe'copendiiig patentapplication of R. C. Mathes, SerialNoJ 370,03 mentioned above, which terminal. circuit is applicable to' cable' systems'in which a V the two-way cable betweenterininals is comparatively short or of such low attenuation that it is feasible to select the courier'con' trol currents 1n the presence of s multane-v. p I

branches thereof: a wave-controlled, relayously outgoing speech energy:

The terminalstationi of t'he drawing coinpr ses connected between a tWQrWftY speech wave transmission circuit TL whichn ay; be

a-telephone line, and a two-way cable TC or high attenuation andhigh transmissiontime constant, such as a. deep sea telephone submarine .cable,-r a 1 one-Way:transmitting amplifying Lpath; TA and r a one-way receiving amplifying-path RA. The output of the transniitting path TA and the input of the receiving path are connected to the east end ofthe cable .TG by means oi a three Winding transformer or hybrid coil H which cooperates with the balancing network N in well known manner to insure substantial conjugacy-between the paths TA and RA. For a similar purpose the inputof the r V transmitting path TA and the output of the receivingpath RA are connected to the circuit TL through'the hybrid coil H having an associatedbalancing network H a Qonnectedbetvvecn the hybrid coils H H inZ-the one-way transmittingipath TA is a delay circuit 1 a'iida One-Way transmitting amplifier 2, and, connectedtbetween the hybrid coils H and H in the receiving path RA, isa band, pass filter 3 and a one-way receiving amplifier 4. Connected across the path TA between the hybrid coil H and the input of delaycircuit l is va control circuit 5 comprising a wave-controlled, relay.- controlling fdevice 6,;and the :windings of relays 7 and 8t-connected inparallel to the {output of the device 6; The relay 8 is slow operating as compared to the relay 7.

, A source 9 of alternating current of frequencies outside the signal frequency range, which inthe case being described is the speech frequency range, is adapted to be momentarily connected across the .transmitting'pathjTA at the points 10 between the output of the delay circuit 1 andthe in- A put of'the transmitting amplifierfl by means of switches 11 and-12, respectively controlled by operation'o'f relays 7 and '8 tlonnected across the transmitting path. TA between the points 10 therein and the input of the transmitting amplifier 2 is a second control circuit 13 comprising a-delay circuit 1A, a

wavercontrolled, relay-controlling device 15 and one winding of a three-winding relay 16 connected to the output of the device 15.

Connected across the control circuit 13 in the output of the delay circuit 14 therein is a third control circuit 17' comprising the delay circuit 18, the wave-controlled, relaycontr ollin-g device '19, the 'win ding of a relay 20 and a second Winding of the relay. 16

betenpla'ined, andthe windingsrof relays 26 to 31 connected in parallel to output of the device25. ltelayfil is designed so that jit'will operate at a given instant of time later than relays 26 to 80, and so that it will remain operated longer than the latter relays, in responseto the operation ofthe device25.

The output of the device 6 in control circuit 5 is adapted to be connected through a cir'cuitilZto the third'windingot the relay 16. Relay 16 is constructed so that energization ofany one of its three windings will cause therelay to operate. 1

- ln' thelinput of the transmitting path TA between the point of connection thereto of control circuit 5 and the hybrid coil H is a normally closed switch 3% adapted to be opened by operation o of relay 29' to disable theinput ofthe path TA, and in the transmitting path TA between the point of connection of the control circuit- 18 thereto and the input of the amplifier 2, is a normally closed switch 35 adapted tofbe' opened by operation of relay 28 to disablethe output of the path TA. Tirthe receiving path RA between the output of the amplifier 4 therein and the hybrid coil H is'a normallyvopen switch 36 adapted to be closed byoperation of relay27 to make the path RA operative. Inthe output or filter Qalin the lower parallel branch of control circuit 22 is a normally open switch37 adapted to be closed by operation of relay 26 to'connect'the output of filter 24lto the input of the device ln control circuit QQbetWeen the point of con nectiono'f relay-- ill-thereto and the relays 26 to is a norniall closed switch 38 adapted to be opened by operation of relaylfi to dis t able the inputofrelays-26 to 30.

1,-sao.22e

. adapted to be opened by operation of relay" 30130 disable the input ofzonewinding of rel ay 16. In the output of control circuit 17 is a normally closed switch 41 adapted to be opened also by operation of relay 30 to disable theinput ofanother winding of relay 1 6. In the circuit 32is a normally closedswitch 42 adapted to be opened-also by operation of relay 30 to disable the'inputto the third winding ofrelay 16. Inthe circuit-32cmneoting the output of the'device 6 in control circuit 5 to relay 16 is a normally open switch 43adapted to be closedby operation of the relay 31 to enable the thirdwinding. of relay trol' device "6.

16;.to be energized through operation ofcon The wavekcontrolled,relay-con l vices, 6, 15,19; and 25, and the corresponding devl'cesat the westterminal station, may be vacuum tube, amplifierrrectiiier :devices of theLtype-well knownin theart, or any other devices which will respond to alternating currentwaves impressed. ontheiri nputs to control the operation of circuit-control devices, such asmechanical relays in their outputs.=- Tlhedelay circuits 1,14 and 18 maybe networks of any type suitable for producing a delay in the transmission therethrongh of ing speech waves. The delay circuit 1 1 and the alternating current waves impressed on their j inputs; for example they maybe lowpass to enable the completionof the operationzo'f the circuitcontrol relays by a preceding courier impulsetocondition the speech trans mission paths-for transmission of thefollow corresponding delay'circuit at the west terminaly stat-ion are {designed to produce a time delay of T-t in the transmission; of alternating currentwaves therethro-ugh, T beingv substantially equal to the overall transmission time of thecable TC betweenthe east and the;

I west terminalstation. The delay. circuit 18 and thej corresponding delay circuit the I west terminal station are designed to produce a time delay of Tin thetransmission ornternatingi current waves theretlirough.

Thefilters 3, 23 and24i and the corresponding filters at the west terminal'station may be of thebandpass typefdisc'losedin the U. S.

. patents to Campbell mentioned above. The

filters3 and 24 and the corresponding filters atTtli'e west terminal station-are designed to transmit frequencies within the speech ,fre-

trolling de;

quency range. Filter 23 at the east terminal station. is designed topass the courier frequenoies f generated by the courier genera: tor at the west terminal station corresponding to generator 9 at the eas; terminal station and to suppress the frequencies f corresponding to those generated by the generator 9 at the east terminal station, f and f being different frequencies outside the speech frequency range. The filter at the west terminal station corresponding to the filter 23 at the east terminalstation is designed to pass waves of frequencies corresponding to the courier frequencies f generated byv the courier generator .9 at the east terminal station and to suppress the frequencies f corre spending to the courier frequencies generated by the cour er generatorat the west termithe courier generator 9 and the relays 7, 8, 16, 20 and 26 to 31 at the east terminal station and thecorresponding apparatus at the west be of any of the types in either direction the switches at both terminalstations are in the condition indicated atithe east terminal station in the drawing. The, transmitting ampllfying paths at both terminal stations are then operative and the receiving path at both terminals inoperative.

It will be assumed that speech waves from a subscriber associated with the telephone circuit TL to be transmitted over the cable TC in the direction from east to west are being received at the east terminal station over the telephone circuit TL, and at that time no speech waves from the subscriber associated with thetelephone circuit'at the west termi nal station corresponding to the circuit TL at the eaststation to betransmitted over the cable TC from west to east are being received at the west terminal station. The speech waves received over the circuitTL are impressed by the hybrid coil H on the transmitting-path TA at the east terminal station and willbe divided therein between the input of the delay circuit-1 and the input of the control device ,6 in control circuit 5. The portion diverted into control circuit 5 will operate the control device 6 therein causing the windings of relays and 8 to be energized- The relay 7 will operate quickly to close the switch 11 to connect the source 9 of courier waves of frequencies 2 across the transmitting path TA'at the points 10 in the output of delay c":cuit 1, and the comparatively slow operat ing relay 8 will operate a given inst-ant later to open the switch 12'so asto disconnect the'generator 9 from the transmitting path The momentary connection of the generator 9. to the transmitting'path TA will nal station. The one-way amplifiers 2 and a,

cause a short train of waves of frequencies f 1 which will be referred to hereinafter as the courier 72, to be transmitted over the trans ing that circuit inoperative to cause false mitting path TA. This train of waves may be made as short as is desired or is'necessary bythe relativedesign of relays 7 and 8. 'Relays 7 and 8 are also so designed that they will remain operated as long as-speech waves from the circuit TL are being impressed on the input of control device 6, and so'that they will releaseonly after a complete pause in the continuoustransmission of the impressed speech currents, for example, at the .end'of.

the -sentence, andnot. for the usual short pausesbetween words or syllables.

" 'Aportion of the-courier will be ampli- 1 fied by the transmitting amplifier 2 and the amplified Waves impressed by the hybrid coil 'Hi'upon the cable TC over which'it will be transmitted to the west terminal station-to establish initial control of the circuit control apparatus thereat'in a manner which will be described later. 7

Another portion of the courier f is diverted from thetransmitting amplifying path TA. into the control circuit 13 and willbe delayed in transmission therethrough by the delay circuit 14: for a time T-z where, as

indicated before, T is the overall transmission time of the cable TC between the terminal stations and t is equivalent tothe delay produced in the transmission of the speech,

currents by the delay circuit 1 in transmitting path TA. In the output of the delay circuit lt the courier 72 will be divided be tween the-control circuits 13 and 17. The portion transmitted through-the control circuit 13 will operate the control device 15 therein which in turn will energize one wind-v ing of relay 16'. Relay 16 will then operate to open the normally closed switch'88 inithe receiving controlcircuit 22 thereby render operation of relays 26, to30 due to l'aterOperationcf' control device 25 by incoming waves received from the west terminal star" tion; The first talker, that is, the subscriber connected to the telephone lineTL, has now 66 under the control of control device 19 over the circuit 17 instead of under the control of control device-15 in control circuit 13. This obtained absolute control of the east terminal station. i The portion of the courier f transmitted into the control circuit l7 will delayed in 7 transmission therethrough for an additional time interval Tand then will operate control device 19 to apply energizing current to the" winding of relay 20, and to one windingof" relay 16 over thecircuit 17. Relay 20 will.

operate to open the normally clo'sedswitch 39in the inputofcontrol circuit 13, thereby disabling control device 15. Relaylfi is then rearrangement of the controlling circuits at the east statlonin the manner which will be explained below will enable, alistening subscriber at the west terminal station to break in onlthe talking subscriber and to seize abthe transmission:pathfTA. The main portion ofthe speech currents will be trans- 'mitted f rom .th-e output of the dela circuit 1 in'the transmitting path TA- to the input of the transmitting amplifier 2 therein, and will be amplified by that amplifier and impressed. on the cable TO by the hybrid coil H The impressed speech waves will then be transmitted" over the cable TC following the previously transrhittedcoUrier f by the time interval t.

' The manner in which control of the transmitting and receiving circuits and the associated control circuitsat the west terminal stationis also obtained for the first talker associated with the east station will now be described by reference to the similar apparatus at the east terminal station shown in the drawing. That the apparatus to be referred to at the west terminal station is that of the west terminal station will be indicated by designating the apparatus thereat with the same characters which designate the corresponding apparatus at the'east terminal stationbut followed by a prime mark.

Because of the time delay of Tt intro- 5 duc ed by the delay circuit 14 in control circuit 13. of the eastjtermina'l station in the transmission of the portion ofthe talkers courier f diverted therein, the other portion ofthe talkers courier f arrives at the west terminal station overthe c'able T'C (which has an overall transmission time of T) at about the time the portionof the courier f cause the relay 16 to disablethe output of the circuit'22 by opening switch 38 therein. 7

The portion of the courier f received over the cable TC will be impressed by the hybrid diverted into control circuit-13 at the east station has operated the control device 15 to coil H upon the receiving-amplifying path BA" at the west station. The impressed cou rier f will be divertedinto the control circuit 22 and then will be passedby the band-pass filter "23 in the upper branch thereof and .causeztheinitial operation of'control device 25. The operation of control device 25 will energize the windings oft'he relays 26 to 31". Relay 26 will operate to close the switch 37 in the output of filter 24', enabling a portion or" the speech waves following the band-pass filter 3 courierf with a time delay of t'to'be transmitted through filter 244m the input of the control device and maintain that device in the "operated condition initiated by the preceding courier. The main portion of the speech waves will be transmitted through in the main receiving path RA and willbe amplified by the amplifier 4' therein;

' Relay 2?. will operate to close thenormally openswitch 36 in the output of the receiving path RA, thus rendering that path operativetotransmit the amplified east to west speech waves from the output of amplifier 4 to the hybrid coil'iH which .will impress them on the circuitTL. v

Relays 28 and 29 will operate substantially simultaneously with relays 26 and 27' to open the normally closed switch andtsl" respectively, infthe transmittingamplifying path TA, thus rendering that pat inoperative from that time to transmit any west-toeeast speech waves which may be received overfthe circuit TL" to the cable TC or to'theinputof controldevice 6. Relay 30' will operate substantially simultaneousl with relays 26 to 29" to 'open'the nor mal y closed switch 40 in controljcircuitl3, the normallyclosed switch 41 in control circuit 17; and the normally closed switch 42' in circuiti 82, thus preventingthe relay 16? from being thereafter rendered operative icy-energy which may, befstoredinthe circuits13', 17" and 32 at thetimeswitch 34' opens,fto cause false operation of theswitch 38 to block the receiving control circuit 22,". Boththe east and west terminal "stations are now under complete control of the first talker.

A given instant after relays 26 to 30 have operated, the comparatively slow-operating, slow-releasing relay "31? will, be operated by control device 25' to close the normally open switch 43 in thecircuit32', thus making the latter circuit operative to allow 'zhe operation of control device 6' by the listenersspeech currents tojoperate relay l5 whenever the switch 42 incircuit '32 .5 closed. 1 i

'lirom the above descriptionit is'seen that at 1 time after the courier has been sent out from the east terminal station substantially equal to the overall transmission time T of ;he cable TC between thelstations, the cir :uits'have beenarranged so that the first alker (the east subscriber) hasobtained com plete controlrof the transmitting and re- :eiving circuits and the associated. control of )oth stations. With the circuits in this conlition the listening subscriber associated vith the west terminal station normally caniot,by'starting to talk, during a pause in the alkers speech, seize control of the system or the transmission of hisown speech cur ents unless this pause continues for a time nterval at least equal tothe' overall transmission time T of the cable, tor will take that interval of time for the listener to transmit his courier/" to the east terminal station. The automatic rearrangement of the control circuits at the transmitting terminal a given intervalof time after complete control of the system has been obtained by the first talker will bias the system so that the listener may obtain, it he desires, exclusive control of the system, the circuits at the east terminal are rearranged by operation of the control device 19 by a portion of the talkers courier f which has been delayed in transmission through control circuits 17 forthe time T by delay circuits 18. The operation of device 19 energizes the relay 20 to open the switch 39 in the input ofcontr'ol device 15 in control circuit 13', disabling that device, and energizes'the blocking relay'16 over the circuit 17. The talkers speech 'waves'following the courier f through the control circuit 17 with a time delay 0ft maintains the device '19 in the operated condition initiated by the courer Meanwhile, at the west terminal station the talkers courier f has, through the operation of control device 25 in receiving control cir- "cuit 22, operated the relay 3l to close the normally open switch a3" in circuit 32'. As stated above, the relay 31 is arranged to opcrate a given time after the operation of the other control relays 26 to 30 and to remain operated for a short time after the latter release. This delay inoperation and hangover maybe obtained by'the mechanical design of relay 31 to make it slow-operating and slow-releasing, as indicated in the draw ing, or the required delay in operation may be obtained by the use of a delay circuit of proper design betweenthe winding of relay 31 and the output of the control device 25. The relay 31 at the east terminal station may be similarly arranged to operatelater than the relays 26 to 30 thereat and'to remain operated longer than the latter relays.

Now suppose that at any time after this rearrangement of the east terminal circuits, that is, subsequent to a time interval T after complete control of both terminals has been obtained by the east talker, the east talker pauses long enough to allow release ofthe relays 28 and 29' at the west station, thereby making the transmitting circuit TA thereat operative during the pause. If the listener starts talking during this pause, he can get v immediatecontrol of the west station controls as the slow-rel ase relay 31 is still operated by the east talkers speech to hold the switch 43 in circuit 32 closed. The west subscribers speech currents diverted into. the control circuit5 will operate the control de- .v-ice 6, which in aims-111 cause the operation of relay 16' through circuit 82' to blockthe receiving control circuit 2% by opening the slow'jrelea'serelay' 31 has released to disable switch 38. The operation of the controlcircuit' 6 will also control the operation of relays 7 and-8i to send-a courier impulse of frequency from generator 9 out over the transmitting path TA to the cable TC. A portion of the courier f and the following speech waves diverted into control path 13 control device 15 and later control device 19 to maintain therelay 16 operated after the the circuit 32.

The portionof the listeners courier f transmitted over-the cable .TC to the east described inconnection with the. courier westterm'inal to release.

terminal station will arrive there when'the switch 38 in the control circuit 22 thereat is closed due to the release of relay 16 during the same pause in the east subscribers speech that allowed the control relaysfat' the Theswitcjh 38 being closed when the courier 0pQI,ltQS'GOI'llZIOl'dGYlCB 25, the latter dcv1ce willcause operation of relays 26 to 31 to seize control" of theeastterminal for the west'subscriber in aflmanner similar to that I I H .at ,:the west terminal station.

,The talkingsubscriber associated with the .west terminal, thaltis, the former listener,

i fhasnow obtained control of both terminal.

:10 7 as regards subsequent transmission control stations and will normally be able to exclul sivelyf'control the-stations for transmission of his own speech currents to the east subiSCriber, until a time T later when the circuitat the west terminal will be rearranged .automaticallyv in amanner similar to that which has been described in connection with the east terminal station, to bias the system in favor of the subscriberassociated with the east terminal who is now the listener.

I All of the control relays in the systemwhich has gust been described, should be designed to have such hangovers, in their operation as to msure their release only after the dissipation of any speechw-hich the subscriber who does not control the system may have transmitted.

It is apparent from the above description that the circuits at the east and west ter-'.

1 minals of the systemv are such as to enable a subscriber associated with either: terminal,

' a given time after the first talker associated with another terminal has obtained complete control of the talking circuits of the system, to interrupt-the speaker'a-t the least pausein the latters continuous transmission of sp.eech,1for example, a pause between words. This will enable considerable speediiig :up of a two-way conversation between subscribers overalong cable system. 1

' Although in the particular embodiment of the invention described mechanical relays have been shown for conditioning the trans mission pathsfor operatingmovable switches to close or open circuit these paths the 1nv'ention is not limited to. the particular conditioning means shown. For example, within, the scope of the invention thetransinission paths 'may' be effectively disabledor made operative by the insertionor removal of short circuits or loss networks in thepaths controlled by wavecontrol apparatus. Stationary devices having no movable elements may be employed in place of the mechanical relays shown, for example, vacuum tube. relays,- such asdisclosedzin Crisson Patent 1,647,212 issuedNovember 1, 1927 or in an article by C. A. Beers and G. T. Evans in the Institute of P. 0. Electrical Engineers (Londonlvol. 20, pages 65 to .72 inclusive, published in:192"0. V

It is to be understood that the invention is not limited to the exact detailsof thecircuits in theterminal stations illustrated and described, as numerous modifications thereof may be ma-de by persons skilled in the art without departing from .thespirit 'and scope of the invention. p 4

What is claimed is: I v

1. 'Asystem for transmitting signals in opposite directions betweenstations, comprising means. normally preventing transmission -.of signals betweensaid stations in either directiommeans responsive to the initiation of signals atone of saidstations for rendering the system" operative to transmit saidsignals toanother station while preventing transmission of. later initiated signals fromsaid other station to said one station andmeans also responsive to the signals initiated at said one station for altering the circuit connections thereat to bias the-system as regards subsequent directional control of transmission in favor of later initiated si nals at said other station.

2'. A system for transmitting signals in opposite directions between stations, comprising means normally preventing signal transmission in either direction between stations. means responsive to the initiation of signals at one of saidstations for rendering thesystem operative to transmitsaid signals to another station, while preventing transmission of later initiated signals from said ether tion to said onestatioin-and. means also responsive tothe signals initiated atsa-id one station, and operative "at a predetermined time after their initiatiointo bias said system as regards subsequent directional control oi transmission in favor of later initiated signals at said other station. s

3. system for transmitting signals in opposite directions between stations, comprising means normally preventingsignal transmission between. said stationsineither direction, circuit-controlapparatusat' each station, means ateach station responsive to tin initiation of signals thereat tocontrol the circuit control apparatus at saidstationsto render the system operative toJtransmit said si nals to'another station and to prevent transmission of later initiated signals from said other station to the first station, and means; also responsive to the initiation of said signals at said first station, and at a time thereaftersubstantially equal to twice the overall transmission time of the system between stations, to alter the connectlons to said c1rcu1t-control apparatus at said first station to bias said system as regards subseresponsive to'the telephonic currents of said first subscriber for biasing the circuits at said one station as regards obtaining-subsequent directional control of the system in favor of the second subscriber at said other station.

5. The system of claim 4 and in which said biasing means is responsive to the telephonic currents of said first subscriber at a predetermined time after their initiation.

6. The system of-claim 4 and in which said biasing means is responsive tothe telephonic currents of said. first subscriberat a time after the initiation of said currents substantially equal to twice the overall transmission time 3f the system between said one and said other station.v v

7. A two-way system for transmitting signals between subscribers connected to differant stations comprising means at said sta-, ions-normally preventing transmission between the subscribers in either direction,

neans' responsive to the initiation of signals 3 the subscriber at one station to condition ;he system to transmit said signals to a secmd subscriber at another station while pre- Ienting transmission of signals later ini- ;iated by said second subscriber to the sub- ;criber connected tosaid one station until a predetermined time after a pause in the first nentioned subscribers signals, and means ilso responsive to said first subscribers signals and operative a definite time after-the nitiation thereof, for biasing the system so as 0 enable said second subscriberto break said irstvmenticned subscribers control of the :ystem and to'seize control thereof for the ransmission of his own signals, at a pause n the transmission of signals by the first subscriber. less than said predetermined time. :8. In a two-way telephone systemcomprisiiig two stations connected by a two-way transmission medium, circuit-control means at each station, fandmeans responsive to the speech currentsof thefsubscriber atone station who first starts to talk for controlling said circuit controlmeans to condition the system for the transmission of said speech ci'u rents-ztoa second subscriber at the other station, and to prevent said secondsubscriber from obtaining control of thesystem until a pause of givenlength in the first subscribers transmissiom'means responsive to the first subscribers telephonic currents and operative a definitej time after the first subscriber has. obtained complete control of, the system for altering [the circuit connections of the system so asqto enable thesecond subscriber to immediately seize control of the system for the transmission ofhis own telephonic currents to thegfirst subscriber ata pause-in the. transmission of the first 'subscribers given length. H

9 The'system telephonic currents'oi a length lessthan said of claim 8 and which the lastmentioned means comprises means at' said otherstat on for enabling said second subscr ber to lmmedlatelyse ze controlfofi' the; circuit control meansat said other Sta-- tion. and to send out control waves over said 'medium-tothecirouit control means at said a one station,-,at a slight pause in the continuous. jtransm1ss1on of telephonic currents by said ffirst subscriber.

'10., The systemof claim 8 lastvmentioned means comprises vmeans at said other station for-enabling said second subscriber' to, seize control of the' circuit control means at said other station. and to send out control wavesover said medium to the circuit control means at said one station, at a slight pause in the continuous transmission of telephonic currents by said first subscriber, and means at said one station responsive to the first subscribers telephone currents for changing the connections to the circuit control means at said one station at a time after said first subscriber has obtained complete control of said system substantially equal to the overall transmission time of said medium between said stations, so that said control waves may seize control of said circuit controlmeans thereafter at a path, means responsive to signals from said source transmitted over said transmitting path for controlling sa1d c1rcu1t control and in whichthe,

' means and other meansalso responsive to the signals transmitted over said transmitting, path but operative a predetermined time afterthe first mentioned means for assuming 1' control of-said circuitlc'ontrol means in place f of said-first mentioned-means. V 12. A terminalcircuit fora two-waysignaltransmission line comprising; a transmitting path connected to said liner and supplied is froma source of signals, a receiving pathconnected to said line, circuit control means-insaid receivingpath, means responsive to the signal's from said source transmitted' over said 1 transmitting path for controlling said circuit control means, and other means also responsive tothe signals transmittedover said transmitting-path butoperative a predeter- "mined time afterthe first mentioned controlling'means, for disabling said first mentioned '20; means and assuming'control'of said circuit control, means. a

' 13 In'combi-nationwvith' a two-Way signal 7 transmission circuit; a terminal station com- 7 prising-a transmitting pathand a receiving "pathconnectedjto said two-Way circuit; a

- source of-si'gnals connected-"tosaidtransmitting-'path','means responsive to signals transmitt'edi'rom said source to said transmitting "path for normally disabling said receiving 30: path a predetermined"appreciable time after the initiation 'o'f'said' signals insaid transmitt-in-g path, control means normally inoperati've but adapted hen operative to be respon v sive'to signals from said-source to disable 1 said receiving path substantially at the time of'initiation of'the controlling signals in said transmitting'path, and means responsive to Waves received in said receiving path from said two-Way circuit for rendering said con- 40 trol' means operative. V 1

In Witness whereof, I hereunto subscribe my name this 7th day of J Lily, 1930.

' 'j BJORN G. BJORNSON 

